Hydrazines find a variety of uses in silver halide photography. They have been used in negative working surface latent image forming silver halide emulsions to increase speed and/or contrast. They have been used as nucleating agents in internal latent image forming direct positive emulsions as nucleating agents.
The use of hydrazines in negative working surface latent image forming emulsions to increase speed and contrast is taught by Trivelli et al U.S. Pat. No. 2,419,975. Increased contrast attributable to hydrazines in negative working surface latent image forming emulsions is believed to result from the promotion of infectious development.
Direct positive images can be produced using internal latent image forming emulsions by uniformly exposing the emulsions to light during development. This renders selectively developable the emulsion grains which were not imagewise exposed--that is, those grains which do not contain an internal latent image. Ives U.S. Pat. No. 2,563,785 recognized that the presence of hydrazines during processing can obviate the need for uniform light exposure. Hydrazines so employed with internal latent image forming direct positive emulsions are commonly referred to as nucleating agents (sometimes shortened to "nucleators"). Occasionally the term "fogging agent" is employed, but the term "nucleating agent" is preferred, since nucleating agents do not produce indiscriminate fogging.
The most efficient hydrazines employed in silver halide photographic systems employ a combination of substituents to balance activity and stability. The stability of hydrazines is increased by attaching directly to one of the nitrogen atoms a tertiary carbon atom, such as the carbon atom of an aromatic ring. The art has long recognized that the activity of these stabilized hydrazines can be increased by the direct attachment of an acyl group to the remaining nitrogen atom. Thus, the most commonly employed hydrazines are arylhydrazides.
Arylhydrazides can be incorporated in processing solutions or, preferably, can be introduced directly into photographic elements. Mobile arylhydrazides are preferred for use in processing solutions, but when incorporated in photographic elements the mobility of the arylhydrazides is preferably reduced. This can be achieved by incorporating a ballast. It is also known to incorporate moieties for promoting adsorption to silver halide grain surfaces. When an efficient adsorption promoting moiety is incorporated in an arylhydrazide, the molar concentration of the arylhydrazide can often be reduced by an order of magnitude without loss of activity. Absorbable arylhydrazides are particularly preferred for increasing the speed of negative working silver halide emulsions and nucleation in direct positive emulsions. However, tightly adsorbable arylhydrazides are not usually efficient in increasing the contrast of negative working silver halide emulsions. It is believed that contrast is increased by infectious development and that undue restriction of mobility interferes with the ability of the arylhydrazide to promote infectious development.
The following U.S. Pat. Nos. and other references are illustrative of mobile, ballasted, and adsorbable arylhydrazides employed in processing solutions and incorporated in both negative working and direct positive photographic elements:
P-1 Whitmore: 3,227,552 PA1 P-2 Leone et al: 4,030,925 PA1 P-3 Leone et al: 4,031,127 PA1 P-4 Leone et al: 4,080,207 PA1 P-5 Takada et al: 4,168,977 PA1 P-6 Takada et al: 4,224,401 PA1 P-7 Tsujino et al: 4,245,037 PA1 P-8 Hirano et al: 4,255,511 PA1 P-9 Adachi et al: 4,266,013 PA1 P-10 Nothnagle: 4,269,929 PA1 P-11 Mifune et al: 4,243,739 PA1 P-12 Mifune et al: 4,272,614 PA1 P-13 Leone: 4,276,364 PA1 P-14 Mifune et al: 4,323,643 PA1 RD-1 Research Disclosure, Vol. 151, November 1976, Item 15162. (Note reduction sensitization effect, left column, page 77.) PA1 RD-2 Sidhu et al, Research Disclosure, Vol. 176, December 1978, Item 17626. PA1 (Research Disclosure and Product Licensing Index were publications of Industrial Opportunities Ltd.; Homewell, Havant; Hampshire, P09 1EF, United Kingdom. Research Disclosure is now published at Emsworth Studios, 535 West End Avenue, New York, New York 10024.) PA1 Amino is a secondary or tertiary amino group; PA1 Ar and Ar.sup.1 are arylene groups; PA1 L is a divalent aliphatic linking group; PA1 m and n are 0 or 1; PA1 Hyd is N,N'-hydrazino (i.e., hydrazo); and PA1 Acyl is an acyl group; PA1 with the proviso that Amino is a secondary amino group when Oxy is an aryloxy group and Amino is bonded directly to Ar or Ar.sup.1. PA1 Alkyl is an alkyl substituent. PA1 R and R' are as previously defined.
Although adsorption promoting moieties for arylhydrazides can include heterocyclic ring structures, such as nuclei of cyanine and merocyanine spectral sensitizing dyes, as illustrated by P-4 and RD-2, preferred adsorption promoting moieties are acyclic thioamido moieties--i.e., moieties containing the following grouping: ##STR1## where the thiocarbonyl, --C(S)--, and Amino groups are not part of a ring structure. Particularly preferred thioamido adsorption promoting moieties are acyclic thioureas, such as those illustrated by P-2, P-3, P-8, P-11, and P-13. P-11, which is directed to achieving high contrast, also discloses the use of acyclic thioamido moieties of the following structures: ##STR2## where R.sup.2 is an alkyl substituent (including alkyl and substituted alkyl groups).